How to scale ColorRamps and Gradient Textures properly?
Without any input to your Gradient texture it will be applying the gradient along the x-axis only. I can't tell from your question, but which axis do you want the gradient aligned with? Likely your texture is applying to the 'depth' of your mesh so all you're seeing is the 'front' face at the far end of the gradient.
Add a Texture Coordinate node to feed 'Generated' into the Gradient - and put a Mapping node between the two so you can easily rotate the coordinates as desired.